JPH0128577B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an automatic roasting device for an oven or a toaster, and in particular, a time constant circuit determined by a capacitor and a resistor is used to control the current supply time to a roasting heater. Regarding the configuration that controls the.

[Technical background of the invention and its problems]

In conventional automatic roasting equipment, the roasting time is set and controlled using a mechanical timer using a spring or the like, or an electronic timer using a CR time constant circuit.

However, in this type of automatic roasting equipment, once the roasting time is set, the heating time remains the same no matter how many times it is roasted, so the disadvantage is that when continuously roasting, the degree of roasting differs between the first time and the second time onwards. It was hot. This is because the temperature of the roasting chamber has increased from the second time onwards, so the roasting is overbaked by the time required for the temperature of the roasting chamber to rise compared to the first time.

Therefore, in the case of continuous baking, the instruction manual usually indicates the time for the first and second baking, and the instructions are to be operated accordingly.
There is also a method of preheating only the first time, but either method has the disadvantage that the timer operation is troublesome and is extremely difficult to use.

In order to overcome this drawback, an automatic roasting device that automatically adjusts the time for the first and second roasting is known as described in Japanese Utility Model Publication No. 14057/1983.

This has the circuit structure shown in Figure 1,
When a bread platform (not shown) is operated, power switch 1 is closed by mechanical engagement, and discharge switch 2 is closed.
will be released. Therefore, the diode 4 and the resistors 5 and 6 are turned off at the same time that the heater 3 starts being energized.
Charging of the capacitor 7 is also started via the capacitor 7.

When this charging voltage reaches the primary breakdown voltage V of the transistor 8, the transistor 8 becomes conductive, and a gate current flows through the thyristor 9, which also becomes conductive.

Then, the electromagnetic coil 10 is energized and excited, thereby releasing the mechanical engagement and turning on the power switch 1.
is opened and the discharge switch 2 is closed. Therefore, the power supply to the heater 3 is stopped, and at the same time, the charge in the capacitor 7 starts discharging via the resistor 11.

Here, if the discharge curve of the capacitor 7 is made proportional to the temperature drop time curve of the roasting chamber, in the case of continuous roasting, the capacitor 7 will not complete discharging and will start charging again while the terminal voltage is V ₁ . As a result,
As shown in FIG _. 2, the second and subsequent roasting times _t2 are shorter than the first roasting time t1.

However, this configuration has a drawback that if the second roasting is started immediately after the first roasting is completed, the second roasting will be insufficiently finished.
In other words, in the case of continuous roasting, the temperature of the roasting chamber increases from the second time onwards, so the time required to heat the roasting chamber is not necessary, but no matter how high the temperature of the roasting chamber is, the temperature of the roasting chamber will increase. It takes a certain amount of time to roast objects such as bread. On the other hand, in the configuration described in the above-mentioned Utility Model Publication No. 45-14057, 1
If the interval between the first and second times is short, capacitor 7
This is because the electric discharge is not carried out sufficiently and the roasting time becomes extremely short, making it impossible to secure the above-mentioned fixed time necessary for roasting the object to be roasted.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned drawbacks, and in the case of continuous baking, it takes into account the temperature rise in the roasting chamber during the second and subsequent roasting, and also ensures a certain period of time necessary for roasting the object to be roasted. In addition, the present invention provides an automatic roasting device that achieves the same degree of roasting for the first time and the second and subsequent times.

[Summary of the invention]

The automatic roasting device of the present invention is equipped with a time constant circuit determined by a capacitor and a resistor, and when the terminal voltage of the capacitor reaches a set voltage, the switching circuit operates to cut off the power supply to the roasting heater. The device is characterized in that it includes a set voltage changing circuit that lowers the set voltage to a predetermined value after the switching circuit operates.

[Embodiments of the invention]

Next, one embodiment of the present invention will be described using FIGS. 3 and 4.

Figure 3 is a circuit diagram of the automatic roasting device, and in this figure, 21 is an AC power supply that outputs AC100V.
A heater 23 is connected to this AC power source 21 via a power switch 22. This power switch 22 constitutes a self-holding relay with a relay coil 24, which will be described later.

The heater 23 has a diode 25 and a resistor 2 in parallel.
6. Capacitor 27 and Zener diode 2
A DC constant voltage circuit consisting of 8 is connected.

Between the (+) and (-) terminals of this constant voltage circuit, there is a CR time constant circuit consisting of a series circuit of a resistor 30, a variable resistor 31, and a capacitor 32, and resistors 34 and 3.
A voltage setting circuit 37 consisting of 5 and 36 is connected in parallel. Further, a series circuit of a resistor 38 and a thyristor 39 is connected in parallel to the capacitor 32. The gate of this thyristor 39 is resistor 4
0 to the (-) end.

41 is a comparator, and one input terminal has a variable resistor 3.
1 and a capacitor 32, and the other input terminal is connected to a connection point between resistors 34 and 35. The output terminal of this comparator 41 is connected via a resistor 42 to the base of a transistor 43 serving as a first switching circuit. The collector of this transistor 43 is connected to the (+) terminal via a parallel circuit of a relay coil 24 and a diode 44, to the gate of a thyristor 39 via a resistor 45, and further to a second switching circuit 46.

This second switching circuit 46 includes a resistor 36
A transistor 47, resistors 48, 49,
It is composed of a capacitor 50, a Zener diode 51, and a diode 52.

This second switching circuit 46 and voltage setting circuit 37 constitute a set voltage changing circuit 53.

Next, the operation of this embodiment will be explained.

First, when the power switch 22 is manually closed, the heater 23 starts to be energized, and at the same time, a constant voltage circuit generates a DC constant voltage across the (+) and (-) terminals. Then, the charging terminal voltage v _a (t) of the capacitor 32 is input to one end of the comparator 41, and the set voltage determined by the resistors 34, 35, and 36 is input to the other end. This set voltage V ₁ is the DC constant voltage E, and the values of resistors 34, 35, and 36, respectively.
Assuming R ₁ , R ₂ , and R ₃ , V ₁ =E(R ₂ +R ₃ )/(R ₁ +R ₂ +R ₃ ).

Here, since the terminal voltage v _a (t) of the capacitor 32 is 0V when the power switch 22 is closed, the output of the comparator 41 becomes "H" level.
Transistor 43 becomes conductive. Then, the relay coil 24 is excited, the power switch 22 is self-held, and the heater 23 continues to be energized.
Further, since the collector of the transistor 43 is at the "L" level, the thyristor 39 maintains a non-conducting state, and the capacitor 32 is charged via the resistor 30 and the variable resistor 31. Further, transistor 47 also remains non-conductive.

Then, _t1 hours have passed since the power switch 22 was closed, and the terminal voltage v _a (t ₁ ) of the capacitor 32 becomes v _a (t ₁ )=E(R ₂ +R ₃ )/(R ₁ +R ₂ +R ₃ ), the output of the comparator 41 is inverted and becomes the "L" level.

Then, the transistor 43 becomes non-conductive, the power supply to the relay coil 24 is cut off, and the power switch 22 is released from its holding state and becomes open.
Power supply to 3 is stopped.

Furthermore, when the transistor 43 becomes non-conductive, the collector changes from the "L" level to the "H" level. Then, the thyristor 39 via the resistor 45
is turned on, and the charge in the capacitor 32 is instantly discharged via the resistor 38 and the thyristor 39. At the same time, the second switching circuit 4
The capacitor 50 of No. 6 is instantly charged via the diode 52 and the resistor 49 to a constant voltage defined by the Zener diode 51.

Next, when the power switch 22 is closed again after a short interval time _t0 , power supply to the heater 23 is started as in the first time, and the comparator 4
The output of the transistor 1 becomes "H" level, which makes the transistor 43 conductive, and the relay coil 24
energization is started and the power switch 22 is self-maintained.

However, the difference here from the first time is that
Since the capacitor 50 is charged, the base voltage is applied to the transistor 47 via the resistor 48, and the transistor 47 becomes conductive.
Resistor 36 will be shorted. Therefore, unlike the first time, the set voltage of V ₂ =ER ₂ /(R ₁ +R ₂ ) is input to the other end of the comparator 41. Since this set voltage V ₂ satisfies V ₂ <V ₁ , if the terminal voltage of the capacitor 32 at this time is v _a (t ₂ ), then v _a (t ₂ ) < v _a (t ₁ ).

Therefore, the terminal voltage of the capacitor 32 is v _a (t ₂ )
The time t ₂ required for this to occur is also shorter than t ₁ . This relationship is shown in FIG.

In this way, from the second time onward, the charging time of the capacitor 32, that is, the roasting time, becomes shorter by a certain period of time than the first time. By making this shorter time, that is, the time t ₁ −t ₂ , correspond to the preheating time of the roasting chamber, the degree of baking of the object to be roasted for the first time and after the second time can be made equal.

Note that the charge in the capacitor 50 is transferred to the resistor 48 having a large resistance value and the gate of the transistor 47.
It is gradually discharged through the emitters. Therefore, by appropriately selecting the discharge time constant in relation to the cooling of the roasting chamber, it is possible to Since the capacitor 50 has completed discharging and the transistor 47 is in a non-conducting state, the set voltage becomes V ₁ again and the firing time becomes t ₁ which is the same as the first time.

In addition, by changing the value of the variable resistor 31,
The time constant of the CR time constant circuit changes, which allows the roasting time to be changed.

In the above embodiment, in order to lower the set voltage from the second time onwards, the resistor 36 is short-circuited by the transistor 47. However, the present invention is not limited to this. It is also possible to have a configuration in which a short-circuit is established using a switching circuit, and this switching circuit is made non-conductive from the second time onwards.

〔Effect of the invention〕

According to the invention, in the case of continuous baking, the set voltage is lowered to a predetermined value by the set voltage changing circuit from the second time onward, so that the capacitor charging time, that is, the roasting time, can be shortened by the time required to heat the roasting chamber. It is possible to prevent over-baking of the roasted items after the first roasting, and even if the interval between successive roasting becomes very short, it is possible to secure a certain amount of time necessary for roasting the roasted items, and the roasting time between the first and second roasting can be improved. The conditions can be the same.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional automatic roasting device, FIG. 2 is an explanatory diagram of the operation of FIG. 1, FIG. 3 is a circuit diagram showing an embodiment of the automatic roasting device of the present invention, and FIG. FIG. 4 is an explanatory diagram of the operation of FIG. 3; 23... Heater, 30... Resistor, 31... Variable resistor, 32... Capacitor, 37... Voltage setting circuit, 43... Transistor as a switching circuit, 53... Setting voltage changing circuit.

Claims (1)

[Claims] 1. In an automatic roasting apparatus that is equipped with a time constant circuit determined by a capacitor and a resistor, and when the terminal voltage of the capacitor reaches a set voltage, the switching circuit operates and cuts off the electricity to the roasting heater. An automatic roasting device further comprising a set voltage changing circuit that lowers the set voltage to a predetermined value.